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04-15-2011, 06:48 AM   #1
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pentax m smc 50mm f1.4 - aperture problem

hello there
until yesterday, my manual lens failed to stop down, when i rotate the aperture ring. the ring clicks over all the way to f22 but the aperture blades remains wide open, on my pentak kr.
i took the lens off, checked & it seems everything worked fine. re-engage back on the body, whilst rotating to lock lens in, the aperture blades gradually open until full open when lens is locked in.
further investigation, i found the aperture lever, next to the mount is actually catching on the camera body. i can see score marks on the body ( 12 o'clock position on pix)
i'm not sure what's going on, given this lens being working fine since i got it back in feb2011. tested on another camera body( demo at shop). problem was still there. hence, this is telling me it's the lens & not the body.
i got a feeling the aperture lever has dropped 0.5mm & causing it the foul against the body. ( pix attached).

my question: do i cut this lever off or is there an adjustment i can do to rectify problem.

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04-15-2011, 08:08 AM   #2
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Are you familiar with how manual lens work on modern DSLR's? The aperture is *supposed* to stay wide open until you actually take the shot (or do a "Green button" metering or DOF preview). And it always stays wide open in all modes but "M". See the article on how to use manual lenses for more if any of this is new to you:

https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-manua...7-k-x-etc.html

But if you mean it stays wide open even when you take the shot, and you have verified you are in M mode, then indeed, sounds like a problem.
04-15-2011, 08:10 AM   #3
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DO NOT cut the lever. I don't see the scratches to the camera that a aperture lever would cause in the pic of the camera body. Try a test. Mount the lens and adjust the aperture ring to f/5.6. Turn the K-R on.
Set the 'using aperture ring' to permitted in the menu, and set 'Green button' to optical preview, IMPORTANT.
Set the K-R to manual mode, push and release the green button and then take a picture.
Set the aperture ring to f/11, do not push the green button, and take a picture.
Set the aperture ring to f/2, do not push the green button, and take a picture.
Review the pics. If you see a change in exposure, your lens and camera are working.
04-15-2011, 09:52 AM   #4
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Original Poster
hello gp1806,
you're a genius. thankyou. it works. i'm a happy man. i love this lens. it's super sharp f2.8, so sharp that i've to digitally soften the image on a few photos.

i still couldn't workout why the shots i took last night did not response to aperture step down. Furthermore the greenbutton ( was set on optical) didn't click last night either.
perhaps the camera is playing up?? who knows. i will perservere

04-15-2011, 08:35 PM   #5
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Thanks.
I'd bet the camera in the shop didn't have the 'using aperture ring' set to permitted in the menu.
04-16-2011, 03:35 AM   #6
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Original Poster
didn't go that far to check permit aperture ring at the shop.
just had to confirm the cause wasn't the camera.

my camera has been set to allow aperture ring since i acquired this lens. so nothing's changed.
i've been using this lens for 2 months, also on the last weekend. straight back into the bag after the weekend until the other day, when it just won't stop down. this really got me baffled.

nevertheless it's back to OK now. turn it on today, no problems.
this is one of my favourite lens. never leave home without it.

thanks again.

cheers jk
04-16-2011, 05:21 PM   #7
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found the problem. had a good read on the manual booklet.
i may have accidentally rotate top the dial to AV mode. tried this this morning.....it performed exactly as the other day with no control on aperture ring.

don't blame the camera or lens, just blame it on the operator ( me!)

at least i know now.

cheers
10-19-2013, 09:13 AM   #8
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Pentax ME

Hi guys, I got this beautiful old ME from my father, but I'm having the same problem, what should I do, I really love this camera, when I attach the lens the aperture goes to the max, but when I detach it the lens works normally?? Can anyone help me?

10-19-2013, 09:06 PM   #9
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This is normal with all Pentax K-Mount film cameras. The lens will only stop down when the exposure is taken or the depth-of-field preview button (if any - not all models have one) is pressed.

You can test this without film in the body. Just cock the winding lever, set a small aperture or slow shutter speed and look through the front of the lens as you press the shutter button. You should see the lens stop-down.

A copy of the manual can be found here:
http://www.cameramanuals.org/pentax_pdf/pentax_me.pdf
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